Kinematic pair

A connection between two machine links that permits specified relative motion while constraining other motion. Its geometry and contact conditions determine the motion allowed.

Kinematics: The study of motion described without considering the forces that cause it. A kinematic pair is a basic element in the analysis of constrained motion.
Lower pair: A kinematic pair whose links have surface contact during relative motion. Surface contact is one major way a pair constrains relative motion.
Four-bar linkage: A closed chain of four rigid links connected by four revolute joints. Its joints form a simple mechanism built entirely from rotational pairs.
Kinematic chain: An arrangement of links connected by joints that permits relative motion. A chain is an assembly of pairs rather than one connection between two links.
Rigid body: An idealized body whose shape and size remain unchanged during motion. Machine links are commonly modeled as rigid bodies joined by kinematic pairs.
Higher pair: A kinematic pair whose links meet at a point or along a line during relative motion. Point or line contact distinguishes this class from surface-contact pairs.
Slider-crank mechanism: A mechanism that converts rotation into reciprocating translation, or the reverse. It combines revolute and sliding pairs to transform motion.
Kinematic diagram: A simplified drawing that represents a mechanism's links and joints without detailed shapes. It depicts pairs by their motion constraints instead of their physical construction.
Degree of freedom: An independent coordinate needed to specify a system's configuration. The pair's constraints determine how many relative coordinates remain free.
Revolute joint: A joint that permits rotation about one fixed axis while preventing other relative motion. It realizes a pair with one rotational degree of freedom.

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Multibody systemBroader topic: Kinematic pairs specify which relative motions connected bodies can make.